THE MEDIA CENTER

Analysis of dyeing wastewater treatment technology

2017.09.04 09:01

At present, the domestic printing and dyeing wastewater treatment methods are mainly biochemical method, and some chemical methods and physical methods in tandem with them. From the three aspects of physical, chemical and biological methods, this paper introduces the methods, status and development trend of dyeing wastewater treatment at home and abroad.

Physical treatment

The physical treatment method is the most widely used adsorption method, this method is made of activated carbon, clay and other porous material powder or granules mixed with wastewater, or let the waste water through the filter bed by the granular composition, the pollutants in wastewater was removed by adsorption in porous material on the surface or by filtration.

At present, mainly by activated carbon adsorption method, this method is very effective for the removal of dissolved organic matter in water, but it can't remove the dye and hydrophobic colloid in water, and it is only for cationic dyes, direct dyes, acid dyes, reactive dyes and other water-soluble dye has good adsorption properties. The adsorption rate, BOD, removal rate and COD removal rate of activated carbon reached 93%, 92% and 63%, respectively. The adsorption capacity of activated carbon can reach 500mgCOD/g carbon. If the sewage is aerated first, the adsorption rate will be accelerated. But if the waste water is BOD〉200mg/L, it is uneconomical to use this method.

Adsorbent used in a variety of adsorption, the project should consider the adsorbent to dye selectivity, should be based on the quality of wastewater to select adsorbent. The results show that the removal rate of anionic dyes can reach 95%-100% by using silicon polymer as adsorbent in pH=12 printing and dyeing wastewater. Kaolin is also an adsorbent. Studies have shown that kaolin can effectively adsorb yellow direct dyes in wastewater by long chain organic cation treatment.

In addition, domestic activated diatomite and cinder are also used to treat traditional printing and dyeing wastewater. The cost is lower and the decoloration effect is better. The disadvantage is that the amount of sludge is large and the treatment is difficult.

Chemical treatment

There are two kinds of chemical treatment methods for printing and dyeing wastewater, coagulation and oxidation. They have their respective effects in water treatment.

Coagulation method

Coagulation sedimentation and coagulation air flotation are the main methods. Most of the coagulants used are mainly aluminum salt or iron salt, in which the basic aluminum chloride (PAC) has better adsorption performance, while ferrous sulfate is the lowest. In recent years, there are more and more enterprises using polymer coagulants abroad, and there is a tendency to replace inorganic coagulants. But in China, because of the price and other reasons, the use of high polymer coagulant is still relatively small. It is understood that the weak anionic polymer coagulant is the most widely used, and if combined with aluminum sulfate, it can play a better effect.

The main advantage of coagulation is a simple process, convenient operation and management, equipment investment, small occupation area, high decolorization efficiency on hydrophobic; disadvantage is the high operating cost and the amount of sludge and dewatering difficulties, poor treatment effect of hydrophilic dyes.

oxidation process

Ozone oxidation and photooxidation are the main methods. Ozone oxidation is widely used in many countries. Research shows that the ozone dosage of 0.886gOdg dye, light brown dye wastewater decolorization rate was 80%; the study also found that the continuous operation required amount of ozone is higher than that of intermittent operation required amount of ozone, and the reactor installation clapboard, can reduce the amount of ozone 16.7%. Therefore, decolorization by ozone oxidation should be designed as a reactor for intermittent operation, and a separator may be considered in the reactor. Ozone oxidation can get good decoloration effect for most dyes, but it has poor decoloration effect for such dyes as sulfur, reducing and coating. From the domestic and international operation experience and the result, this method has good decoloration effect, but it consumes more power and has some difficulties in large-scale application.

The decoloration efficiency of dyeing wastewater is higher by light oxidation process, but the equipment investment and power consumption need to be further reduced.

Electrolytic process

Electrolytic treatment of dyeing wastewater containing acid dyes has a good treatment effect, the decolorization rate is 50%-70%, but the treatment of wastewater with deep color and high COD is less effective.

According to statistics, the electrochemical properties of various dyes in different electrolytic treatment the COD removal rate was different, the removal rate of COD the size of the order is generally: sulfur dyes, vat dyes, acid dyes, reactive dyes ， neutral dyes, direct dyes with cationic dyes.